全文获取类型
收费全文 | 1890篇 |
免费 | 171篇 |
国内免费 | 457篇 |
专业分类
安全科学 | 176篇 |
废物处理 | 34篇 |
环保管理 | 300篇 |
综合类 | 1205篇 |
基础理论 | 268篇 |
环境理论 | 2篇 |
污染及防治 | 169篇 |
评价与监测 | 65篇 |
社会与环境 | 222篇 |
灾害及防治 | 77篇 |
出版年
2024年 | 4篇 |
2023年 | 31篇 |
2022年 | 44篇 |
2021年 | 53篇 |
2020年 | 60篇 |
2019年 | 67篇 |
2018年 | 54篇 |
2017年 | 93篇 |
2016年 | 91篇 |
2015年 | 95篇 |
2014年 | 99篇 |
2013年 | 169篇 |
2012年 | 178篇 |
2011年 | 172篇 |
2010年 | 138篇 |
2009年 | 143篇 |
2008年 | 100篇 |
2007年 | 143篇 |
2006年 | 136篇 |
2005年 | 98篇 |
2004年 | 77篇 |
2003年 | 57篇 |
2002年 | 73篇 |
2001年 | 43篇 |
2000年 | 37篇 |
1999年 | 40篇 |
1998年 | 24篇 |
1997年 | 29篇 |
1996年 | 26篇 |
1995年 | 31篇 |
1994年 | 16篇 |
1993年 | 16篇 |
1992年 | 17篇 |
1991年 | 18篇 |
1990年 | 5篇 |
1989年 | 10篇 |
1988年 | 4篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1984年 | 4篇 |
1981年 | 5篇 |
1980年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 2篇 |
1972年 | 2篇 |
1971年 | 1篇 |
1969年 | 1篇 |
排序方式: 共有2518条查询结果,搜索用时 15 毫秒
971.
锅炉烟尘测试中锅炉负荷率的计算方法探讨 总被引:1,自引:1,他引:0
GB5468 -91规定 ,锅炉烟尘测试时 ,必须对锅炉的运行负荷进行测试 ,而实际监测过程中 ,许多锅炉房不具备测试的计量条件 ,为了解决这一问题 ,文章提出利用烟气量和空气过剩系数计算锅炉负荷率。在实际监测工作中 ,该方法方便、易于操作 ,所得结果和标准规定方法所得结果有很好的一致性 相似文献
972.
Altun L Baskent EZ Gunlu A Kadiogullari AI 《Environmental monitoring and assessment》2008,137(1-3):149-161
The productivity of forest sites has been indirectly determined with solo wood production objective in forest management.
Forest site productivity should, however, be determined directly in order to implement ecosystem based multipurpose forest
management philosophy. This article tackles the problem in distinguishing and mapping forest sites using both direct method
and indirect method in Genya Mountain located in central of Artvin State Forest Enterprise. About 112 sample plots were designed
and distributed over the area. In each sample plot, soil samples were collected and the classical timber inventory measurements
were taken. According to direct method, Soil Moisture Regime (SMR) method is preferred due to a water deficiency in the study
area. Water holding capacity was used as an essential criterion for the classification of the forest site. Forest site classifications
were assigned regarding the physiographic factors such as landform, aspect, and slope. Five different forest sites classes;
dry, moderate fresh, fresh, humid and hygric were determined. According to direct method, the guiding curve was used to generate
anamorphic site index (SI) equations and three site index classes; good (SI=I–II), medium (SI=III) and low (SI=IV–V) were
determined. Some important differences between the methods were realized. The forest sites determined with site index estimation
method indicate that site index I and II is 505.99 ha, III 1095.79 ha and IV and V 992.95 ha, whereas forest sites determined
with direct method related to dry site of 937.58 ha, moderate fresh site of 931.90 ha, fresh site of 1,797.71 ha, humid site
of 80.48 ha and hygric site of 356.55 ha. The forest site maps of both methods were created using GIS functions. The forest
sites of open and degraded areas should be determined according to direct method. 相似文献
973.
Visitor use surveys and water quality data indicates that high visitor use levels of two rivers in Puerto Rico does not appear
to adversely affect several water quality parameters. Optimum visitor use to maximize visitor defined satisfaction is a more
constraining limit on visitor use than water quality. Our multiple regression analysis suggests that visitor use of about
150 visitors per day yields the highest level of visitor reported satisfaction, a level that does not appear to affect turbidity
of the river. This high level of visitor use may be related to the gregarious nature of Puerto Ricans and their tolerance
for crowding on this densely populated island. The daily peak visitation model indicates that regulating the number of parking
spaces may be the most effective way to keep visitor use within the social carrying capacity. 相似文献
974.
975.
基于相对资源承载力的可持续发展问题研究——以河北省为例 总被引:1,自引:0,他引:1
采用相对资源承载力的研究思路与计算方法,分别计算出1996—2005年河北省土地资源、经济资源的相对承载力和综合承载力,并分析了其动态变化过程。研究表明:①河北省综合承载力一直处于超载状态,经济资源承载力于2004年后呈现富余状态,经济资源成为河北省的主要承载资源;②与环渤海的其它4省市相比,相对土地资源承载力处于富余状态,相对经济资源承载力处于超载状态;③河北省内11个地市相对资源承载力存在着地区差异。通过河北省相对承载力方面的研究,提出了河北省实现可持续发展的对策与建议。 相似文献
976.
水资源承载力研究进展 总被引:3,自引:0,他引:3
目前,水资源承载力研究主要集中于水资源承载力的各个方面,总体上还没有对其形成一个系统的认识。在总结水资源承载力研究历史和现状的基础上,阐述了水资源承载力的概念与内涵,对其研究方法及存在问题进行了论述,并预测了水资源承载力研究的发展趋势。 相似文献
977.
A method for quick assessment of CO2 storage capacity in closed and semi-closed saline formations 总被引:1,自引:0,他引:1
Quanlin Zhou Jens T. Birkholzer Chin-Fu Tsang Jonny Rutqvist 《International Journal of Greenhouse Gas Control》2008,2(4):626
Saline aquifers of high permeability bounded by overlying/underlying seals may be surrounded laterally by low-permeability zones, possibly caused by natural heterogeneity and/or faulting. Carbon dioxide (CO2) injection into and storage in such “closed” systems with impervious seals, or “semi-closed” systems with non-ideal (low permeability) seals, is different from that in “open” systems, from which the displaced brine can easily escape laterally. In closed or semi-closed systems, the pressure buildup caused by continuous industrial-scale CO2 injection may have a limiting effect on CO2 storage capacity, because geomechanical damage caused by overpressure needs to be avoided. In this research, a simple analytical method was developed for the quick assessment of the CO2 storage capacity in such closed and semi-closed systems. This quick-assessment method is based on the fact that native brine (of an equivalent volume) displaced by the cumulative injected CO2 occupies additional pore volume within the storage formation and the seals, provided by pore and brine compressibility in response to pressure buildup. With non-ideal seals, brine may also leak through the seals into overlying/underlying formations. The quick-assessment method calculates these brine displacement contributions in response to an estimated average pressure buildup in the storage reservoir. The CO2 storage capacity and the transient domain-averaged pressure buildup estimated through the quick-assessment method were compared with the “true” values obtained using detailed numerical simulations of CO2 and brine transport in a two-dimensional radial system. The good agreement indicates that the proposed method can produce reasonable approximations for storage–formation–seal systems of various geometric and hydrogeological properties. 相似文献
978.
污泥龄对A/A/O工艺反硝化除磷的影响 总被引:12,自引:0,他引:12
以实际生活污水培养驯化污泥的小试规模A/A/O工艺为研究对象,进行了污泥龄(SRT)为8、10、12和15 d时对反硝化除磷的影响研究.结果表明,随着污泥龄的延长,反硝化除磷对系统除磷所起的作用越大,反硝化聚磷菌缺氧利用单位PHAs的反硝化数量和吸磷量也迅速增加,聚磷菌好氧利用单位PHAs的吸磷量并没有受到影响,以SRT为12 d时反硝化除磷和系统脱氮除磷效果为最好.结果还表明,去除单位氮所需COD数量随污泥龄的延长呈减少趋势,而去除单位磷所需COD数量呈增大趋势.对于我国典型的城市污水而言,SRT为12 d和15 d时去除单位氮和磷所需的外碳源数量较8 d时要低,从而使反硝化除磷作用可真正地达到节省碳源和能源的目的. 相似文献
979.
可持续发展理念下的地质环境承载力初步探讨 总被引:4,自引:1,他引:3
在环境承载力概念的基础上定义了地质环境承载力,讨论了地质环境承载力的内在涵义及特点,以城市地质环境为例,探讨了地质环境承载力评价的工作程序。 相似文献
980.
基于三角模糊技术的河流水环境容量研究 总被引:1,自引:0,他引:1
基于河流水环境系统的随机性、模糊性特征,以及资料信息的不足和不精确性,将水环境系统参数定义为三角模糊数。在此基础上,通过将常规的确定性模型参量模糊化,建立了河流水环境容量计算模糊模型。根据该模型,可以计算得到三角模糊数形式的河流水环境容量;再由给定的可信度水平要求,可以进一步将水环境容量由三角模糊数转化为区间值。实例研究表明,相对于常规的确定性方法,所得结果更为科学、合理,而且计算简单、操作方便,具有实用价值。 相似文献